Polarization of the Moon as a function of lunar phase in visible and near infrared spectral bands

The polarization state of the Moon varies with both lunar phase angle and wavelength. Knowing the disk-averaged polarization state of the Moon is critical for enabling on-orbit lunar calibration of polarization-sensitive satellite instruments and for understanding passive polarimetric measurements recorded under moonlight illumination. Disk-resolved measurements (i.e., polarization images) provide additional information about the spatial distribution of the polarization state of the Moon which can be correlated with properties of the lunar surface. In this work, polarization images of the Moon were recorded with a calibrated division-of-focal-plane polarization camera, a 300-mm-focal-length lens, and spectral filters with center wavelengths of 450 nm, 520 nm, 650 nm, 800 nm, and 900 nm. The polarization images were used to calculate the disk-averaged degree of linear polarization (DoLP). The polarization extinction ratio ranged from approximately 300 for the shortest wavelength to 50 for the longest wavelength, corresponding to a maximum polarimetric uncertainty ranging from approximately 0.3% to 2%. Measurements were recorded over a phase angle range of -123° to +123°. The disk-averaged DoLP measured for the 450-nm and 520-nm bands agree closely with previously published results, and to the authors’ knowledge, the measurements and resulting fits for the 650-nm, 800-nm, and 900-nm bands provide the first disk-averaged DoLP models for these spectral bands.